It has been the practice for 50 years or more to transfuse whole blood, and more recently blood components, from one or more donors to other persons. With the passage of time and accumulation of research and clinical data, transfusion practices have improved greatly. One aspect of current practice is that whole blood is rarely administered; rather, patients needing red blood cells are given packed red cells (hereinafter PRC), and patients needing platelets are given platelet concentrate. These components are separated from whole blood by centrifuging, the process providing, as a third product, plasma, from which various other useful components are obtained.
In addition to the three above-listed components, whole blood contains white blood cells (known collectively as leukocytes) of various types, of which the most important are granulocytes and lymphocytes. White blood cells provide protection against bacterial and viral infection.
In the mid to late seventies, a number of investigators proposed that granulocytes be separated from donated blood and transfused into patients who lacked them, for example, those whose own cells had been overwhelmed by an infection. In the resulting investigations, it became apparent that this practice is generally harmful, since patients receiving such transfusion developed high fevers, had other adverse reactions, and generally rejected the transfused cells. Further, the transfusion of packed cells or whole blood containing donor leukocytes can be harmful to the recipient in other ways. Some of the viral diseases induced by transfusion therapy, e.g., Cytomegaloviral Inclusion Disease which is a life threatening infection to newborns and debilitated adults, are transmitted by the infusion of homologous leukocytes. Another life-threatening phenomenon affecting immunocompromised patients is Graft versus host disease (GVH); a disease in which the transfused leukocytes actually cause irreversible damage to the blood recipient's organs including the skin, gastrointestinal tract and neurological system. Conventional red cell transfusions have also been indicted as adversely influencing the survival of patients undergoing surgery for malignancy of the large intestine. It is believed that this adverse effect is mediated by the transfusion of agents other than donor red blood cells including the donor's leukocytes.
Removal of leukocytes to sufficiently low levels to prevent the undesired reactions, particularly in packed red cells including those which have been stored for relatively long periods of time, is an objective of this invention.
In the currently used centrifugal methods for separating blood into the three basic fractions (packed red cells, platelet concentrate, and plasma), the leukocytes are present in substantial quantities in both the packed red cells and platelet concentrate fractions. It is now generally accepted that it would be highly desirable to reduce the leukocyte concentration of these blood components to as low a level as possible. While there is no firm criterion, it is generally accepted that many of the undesirable effects of transfusion would be adequately reduced if the leukocyte content were reduced by a factor of about 100 or more prior to administration to the patient. This approximates reducing the total content of leukocytes in a single unit of PRC (the quantity of PRC obtained from a single blood donation) to less than 0.1.times.10.sup.9.